https://purengom.com/2007/07/23/%ec%95%84%eb%ac%b4%eb%a6%ac-%ec%87%bc%eb%a5%bc-%ed%95%b4%eb%9d%bc-%ed%95%b4%eb%8f%84-3g-%ec%95%84%ec%a7%81%ec%9d%80-%ec%93%b0%ec%a7%80%eb%a7%88%ec%8b%ad%ec%8b%9c%ec%98%a4/